This invention relates generally to gas turbine engines and methods and apparatus for decongealing lubricating or fuel fluids in a heat exchanger apparatus in such engines.
Aviation engines use fluids, such as oil or fuel, to dissipate heat from engine components, such as engine bearings, electrical generators, and the like. Heat is typically rejected from the fluid to air by heat exchanger assemblies, such as fuel cooled oil cooler or air cooled surface oil coolers, to maintain oil temperatures at a desired ˜100° F.<T<300° F. In many instances an environment in which the engine may be operated may be as low as −65° F. Problems begin to occur when the engine is in an engine shut down occurrence in the low temperature condition. The oil within the heat exchanger apparatus begins to cool and may become very viscous. As a result, due to the high viscosity of the oil, it does not flow through the heat exchanger apparatus and requires a lengthy period of time to heat up the oil to a desired viscosity for flowing through the heat exchanger apparatus.
Known heat exchanger assemblies have included oil ducts having increased diameter sizing in an attempt to allow for the continued flow of oil therethrough the assembly when operating during low temperature conditions. While these increased diameter ducts may provide for an increase or allowance in flow during low temperature conditions, the ducts are often oversized for normal operating conditions. In addition, these increased diameter ducts are cause of extra weight and bulk to the engine during all conditions of flight.
It would therefore be desirable to provide a robust method and apparatus for maintaining sufficient heating to a lubricating fluid, such as oil, passing through a heat exchanger apparatus during low temperature conditions for an aviation engine that addresses the above issues.